U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 97–4227

Interim Results of Quality-Control Sampling

of Surface Water for the Upper Colorado

River National Water-Quality Assessment

Study Unit, Water Years 1995–96

By Norman E. Spahr and Robert W. Boulger

Denver, Colorado

1997
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Mark Schaefer, Acting Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046
CONTENTS III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction............................................................................................................................................................................ 1

Purpose and Scope....................................................................................................................................................... 3

Acknowledgments ....................................................................................................................................................... 3

Quality-Control Sampling Program....................................................................................................................................... 3

Replicate Samples........................................................................................................................................................ 4

Pre-Processing Split Replicates ......................................................................................................................... 6

Comparison of General Chemical Constituents ...................................................................................... 6

Comparison of Nutrients and Organic Carbon ........................................................................................ 9

Comparison of Trace Elements................................................................................................................ 12

Concurrent and Sequential Replicates ............................................................................................................... 15

Comparison of General Chemical Constituents ...................................................................................... 15

Comparison of Nutrients and Organic Carbon ........................................................................................ 20

Post-Processing Split Replicates........................................................................................................................ 24

Comparison of General Chemical Constituents ...................................................................................... 25

Comparison of Nutrients and Organic Carbon ........................................................................................ 28

Field Blanks ................................................................................................................................................................. 31

General Chemical Constituents ......................................................................................................................... 31

Nutrients and Organic Carbon ........................................................................................................................... 32

Conclusions............................................................................................................................................................................ 34

References Cited.................................................................................................................................................................... 34

FIGURES

1. Map showing location of sampling sites..................................................................................................................... 2

2–5. Graphs showing:

2. Distribution of collection of pre-processing split-replicate samples, 1995–96................................................ 6

3. Distribution of collection of concurrent- and sequential-replicate samples, 1995–96..................................... 15

4. Distribution of collection of post-processing split-replicate samples, 1995–96 .............................................. 25

5. Distribution of collection of field blanks, 1995–96.......................................................................................... 32

TABLES

1. Water-quality monitoring sites in the Upper Colorado River study unit................................................................. 3

2. Distribution of replicate samples............................................................................................................................. 4

3. Distribution of field-blank samples ......................................................................................................................... 5

4. Comparison of environmental and pre-processing split-replicate samples for general

chemical constituents .............................................................................................................................................. 7

5. Summary of differences between environmental and pre-processing split-replicate samples

for general chemical constituents............................................................................................................................ 9

6. Comparisons of environmental and pre-processing split-replicate samples for nutrients and

organic carbon ......................................................................................................................................................... 10

7. Summary of differences between environmental and pre-processing split-replicate samples

for nutrients and organic carbon.............................................................................................................................. 12

8. Comparison of environmental and pre-processing split-replicate samples for trace elements ............................... 13

9. Comparison of environmental and concurrent- and sequential-replicate samples for general

chemical constituents .............................................................................................................................................. 16

10. Summary of differences between environmental and concurrent-replicate samples for general

chemical constituents .............................................................................................................................................. 20

11. Comparison of environmental and concurrent- and sequential-replicate samples for nutrients

and organic carbon .................................................................................................................................................. 21
IV CONTENTS

12. Summary of differences between environmental and concurrent-replicate samples for

nutrients and organic carbon ................................................................................................................................... 24

13. Comparison of post-processing split-replicate samples for general chemical constituents.................................... 26

14. Summary of differences between post-processing split-replicate samples for general

chemical constituents .............................................................................................................................................. 28

15. Comparison of post-processing split-replicate samples for nutrients and organic carbon...................................... 29

16. Summary of differences between post-processing split-replicate samples for nutrients

and organic carbon .................................................................................................................................................. 31

17. Field blanks for general chemical constituents ....................................................................................................... 33

18. Field blanks for nutrients and organic carbon......................................................................................................... 33
Abstract 1

Interim Results of Quality-Control Sampling

of Surface Water for the Upper Colorado

River National Water-Quality Assessment

Study Unit, Water Years 1995–96

By Norman E. Spahr and Robert W. Boulger

Abstract

Quality-control samples provide part

of the information needed to estimate the bias

and variability that result from sample collection,

processing, and analysis. Quality-control samples

of surface water collected for the Upper Colorado

River National Water-Quality Assessment study

unit for water years 1995–96 are presented and

analyzed in this report. The types of qualitycontrol samples collected include pre-processing

split replicates, concurrent replicates, sequential

replicates, post-processing split replicates, and

field blanks.

Analysis of the pre-processing split replicates, concurrent replicates, sequential replicates,

and post-processing split replicates is based on

differences between analytical results of the environmental samples and analytical results of the

quality-control samples. Results of these comparisons indicate that variability introduced by sample

collection, processing, and handling is low and

will not affect interpretation of the environmental

data. The differences for most water-quality

constituents is on the order of plus or minus 1 or 2

lowest rounding units. A lowest rounding unit is

equivalent to the magnitude of the least significant

figure reported for analytical results. The use of

lowest rounding units avoids some of the difficulty in comparing differences between pairs of

samples when concentrations span orders of

magnitude and provides a measure of the practical

significance of the effect of

variability.

Analysis of field-blank quality-control

samples indicates that with the exception of chloride and silica, no systematic contamination of

samples is apparent. Chloride contamination

probably was the result of incomplete rinsing of

the dilute cleaning solution from the outlet ports

of the decaport sample splitter. Silica contamination seems to have been introduced by the blank

water. Sampling and processing procedures for

water year 1997 have been modified as a result

of these analyses.

INTRODUCTION

The Upper Colorado River study unit (UCOL) is

1 of 59 National Water-Quality Assessment

(NAWQA) study units. The long-term goals of

the NAWQA program are to (1) describe current

water-quality conditions for a large part of the

Nation’s freshwater streams, rivers, and aquifers;

(2) describe how water quality is changing over time;

and (3) improve understanding of the primary natural

and human factors that affect water-quality conditions

(Leahy and others, 1990). Hydrologic and waterquality assessments of the UCOL study unit began in

1994. The UCOL study unit is described by Driver

(1994) and Apodaca and others (1996). A network of

14 surface-water-quality sampling stations has been

established in the UCOL study unit (Spahr and others,

1996). Sampling for water-quality constituents began

at three of these sites in water year 1995, and full

implementation of sampling began in water year 1996.

Site locations are shown in figure 1. Site names and

station numbers are listed in table 1. The NAWQA
2 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

program requires that quality-control samples be

collected at sites within the surface-water network

(T.L. Miller, U.S. Geological Survey, written

commun., 1996).

Quality-control samples provide part of the

information needed to estimate the bias and variability

that result from sample collection, processing, and

analysis. The results are used to evaluate possible

effects of bias and variability on the interpretation

of environmental data. Two specific objectives for

evaluating bias and variability are to determine the

extent to which (1) sampling methods and equipment

introduce contaminants (bias) into water-quality

samples; and (2) sample processing and handling

affect the variability of measured constituent concentrations (T.L. Miller, U.S. Geological Survey, written

commun., 1996).

39°

109°

108°

107°

40°

106°

UTAH COLORADO

1

2

3

5

7

11

12

13

 SAMPLING SITE AND NUMBER

EXPLANATION 0 20 40 MILES

38°

0 20 40 KILOMETERS

6

9

9

10

8

14

rand

Junction

Delta

Upper Colorado River Basin 

study unit

Fraser R

Williams Fork Blue

Riv

R

er

Ea iver gle

Roaring Fork River

Dillon

Reservoir

River

4 East River

G

Grand Lake

Lake Granby

RIVER

Glenwood

Crystal River

Taylor River

Tomichi Creek

Gunnison

Blue Mesa

Reservoir

Montrose Uncompahgre River

Gunnison

No. Fork

Roan Creek

COLORADO

Springs

Figure 1. Location of sampling sites (numbers refer to table 1).
QUALITY-CONTROL SAMPLING PROGRAM 3

Purpose and Scope

The objectives of this report are to (1) describe

what factors were considered in the initial qualityassurance sample design; (2) present and describe

quality-control data for water years 1995–96;

(3) analyze the quality-control data for systematic

problems that can be resolved in water year 1997;

and (4) provide insight into operation of the network

for the remainder of the data-collection phase of the

UCOL study unit.

Several types of quality-control samples were

collected during water years 1995–96 and included

pre-processing split replicates, concurrent replicates,

sequential replicates, post-processing split replicates,

and field blanks. Pre-processing split-replicate

samples are samples in which twice the normal

volume of water is collected and then split into two

unique samples before processing. Concurrentreplicate samples are samples that are collected using

two sampling teams or two sets of sampling equipment at the same time. Sequential-replicate samples

are collected sequentially: first one sample is collected

and then a replicate is collected. Post-processing split

replicates are samples that are split after all processing

has been completed but prior to shipment to the laboratory for analysis. A field blank is a sample prepared

using blank water (water that is free of the analytes of

interest), which is passed through all of the sampling

and processing equipment.

Acknowledgments

The authors would like to express thanks

to Jeff Foster, Dave Hartle, and Dennis Smits for

data collection and processing. Dave Mueller and

Terry Schertz provided exceptional technical review of

the manuscript. Thanks also are extended to

Joy Monson (manuscript and layout), Sharon Powers

(illustrations), and Hyla Strickland (editorial review).

QUALITY-CONTROL

SAMPLING PROGRAM

When surface-water sampling began in the

UCOL network, limited information was available

to design the quality-control sampling program.

In the initial and continuously developing qualitycontrol design, several factors were considered, which

included streamflow, expected constituent concentrations, basin characteristics, land use, and whether variability or bias would be important at a site. Variability

is the degree of random error in independent measurements of the same quantity. Replicate samples test for

variability, which could be important at sites that have

high constituent concentrations. Bias is the systematic

error inherent in a method. Blank samples test for bias,

which could be more important at sites having low

constituent concentrations.

Table 1. Water-quality monitoring sites in the Upper Colorado River study unit

Site number

in figure 1

Site

name

Site name used

in this report

USGS station

identifier

1 Colorado River near Colorado-Utah State line State Line 09163500

2 Colorado River near Cameo Cameo 09095500

3 Colorado River near Dotsero Dotsero 09070500

4 Gunnison River near Grand Junction Gunnison near Grand Junction 09152500

5 Gunnison River below Gunnison Tunnel Gunnison Tunnel 09128000

6 Gunnison River at County Road 32 Gunnison at 32 Road 383103106594200

7 East River below Cement Creek East 09112200

8 Gore Creek at mouth Gore 09066510

9 Uncompahgre River near Ridgway Uncompahgre 09146200

10 French Gulch near Breckenridge French 09046530

11 Reed Wash near Mack Reed 09153290

12 Dry Creek at Begonia Road Dry 09149480

13 Dry Fork at upper station near DeBeque Dry Fork 09095300

14 Colorado River below Baker Gulch Baker 09010500
4 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

The distribution of replicate samples is listed

in table 2. The type of replicate sample is based on

design considerations. As data collection started,

concentration ranges for general chemical constituents, nutrients, organic carbon, and trace elements

were determined for each site. Sites within the

network were compared and then categorized as low,

medium, or high based on measured concentrations.

Discharge ranges for each site were defined as low

(base flow), medium (flows above base to about

50 percent of the peak), and high (flows greater than

about 50 percent of the peak). The distribution of

quality-control samples was monitored and adjusted

during the data-collection phase of the project,

producing a dynamic program design. Additional

samples of medium- and high-flow conditions were

needed to balance the overall distribution.

The distribution of field-blank samples and

information for the site sampled before the blank was

processed are listed in table 3. Some field blanks were

processed using equipment that had been cleaned in

the office laboratory. To test the efficiency of the field

cleaning protocol, additional field-blank samples

should be collected following field cleaning rather

than laboratory cleaning. Results of the quality-control

sampling listed in tables 2 and 3 are presented in the

following sections of this report.

Replicate Samples

Replicate samples provide an indication

of the magnitude and source of variability in sample

results. Each type of replicate sample addresses

Table 2. Distribution of replicate samples

[--, no sample]

Site

name

Land

use

Concentration range1

Discharge2

range for

sample

Type of

replicate

sample

General

chemical

constituents

Nutrients

Dissolved

organic

carbon

Suspended

organic

carbon

Trace

elements

State Line Mixed m m m h -- l Concurrent and post-processing split

Cameo Mixed m l m m -- h Concurrent and post-processing split

Dotsero Mixed m l m m -- l Sequential

Gunnison

near Grand

Junction

Mixed m m m m -- l Pre-processing split

Gunnison

Tunnel

Mixed

reference3 l l m l -- h Post-processing split

Gunnison at

32 Road

Mixed l l m m -- h Concurrent and post-processing split

East Rural urban,

recreation

l l l l -- l Concurrent and post-processing split

-- h Concurrent and post-processing split

Gore Rural urban,

recreation

l m m m -- l Pre-processing split

-- l Concurrent and post-processing split

Uncompahgre Mining m l l m l l Pre-processing split

French Mining l l l m h l Pre-processing split

Reed Agriculture h h h h -- m Sequential

Dry Agriculture h h h h -- m Pre-processing split

Dry Fork Reference,

cp4 h l h m -- l Pre-processing split

Baker Reference,

srm4 l l m l -- l Concurrent and post-processing split

-- l Sequential

-- m Pre-processing split

1Concentration ranges with respect to all sites within the surface-water network, l = low, m = medium, h = high.

2Discharge ranges, l = base flow, m = flows above base to about 50 percent of the peak, h = flows greater than about 50 percent of the peak. 3Downstream from major reservoir system.

4Physiographic province, cp = Colorado Plateau, srm = Southern Rocky Mountain.
QUALITY-CONTROL SAMPLING PROGRAM 5

different combinations of sources of variability.

The pre-processing split replicate, the concurrent

and sequential replicate, and the post-processing

split-replicate samples collected in surface water of

the UCOL study unit for water years 1995–96 are

discussed in the following sections.

Data published by the U.S. Geological

Survey are rounded. For example, a calcium value of

150 mg/L (milligrams per liter) is reported (rounded)

to the nearest 10 mg/L. A calcium value of 6.5 mg/L

is rounded to the nearest 0.1 mg/L. Data rounding is

incorporated in the assessment of replicate analysis in

this report by using a unit called the lowest rounding

unit. A lowest rounding unit of 1 would represent

10 mg/L for the 150 mg/L sample and would represent

0.1 mg/L for the 6.5 mg/L sample. A lowest rounding

unit is equal to the magnitude of the least significant

figure reported by the USGS National Water Quality

Laboratory. In this report, the differences between the

environmental and replicate values are given in the

units of the constituent and in lowest rounding units.

The use of lowest rounding units for comparison

avoids skewing comparisons when values of constituents span orders of magnitude. For example, consider

the two pairs of magnesium values for the French

and Dry sites (table 4). The environmental and splitreplicate values for French are 5.5 and 5.6 mg/L,

resulting in a difference of −0.1 mg/L. The Dry environmental and split-replicate values are 36 and

37 mg/L, resulting in a difference of −1 mg/L. Both

of the differences are −1 unit of the least significant

figure or −1 unit of the lowest rounding value. The

practical difference between the environmental and

replicate values is similar in both of these cases (the

only smaller difference available for each pair of

samples would be zero). A comparison of the actual

magnitude difference between the environmental and

split-replicate pairs (−0.1 to −1 mg/L) is of little

use. A difference between the environmental and splitreplicate sample for the Dry site could not be 0.1 mg/L

because the data are reported to the nearest whole

milligram per liter.

Percent differences between the environmental

and replicate values do not yield practical significance

for many of the constituents in this data set. For

example, the chloride environmental and replicate

values for French have a −0.1 mg/L difference

(table 4), which represents a −10 percent difference.

Table 3. Distribution of field-blank samples

[--, no sample or not applicable; lab, office laboratory]

Site Land

use

Previous

site

Concentration range at previous site1

General

chemical

constituents

Nutrients

Dissolved

organic

carbon

Suspended

organic

carbon

Trace

elements

State Line Mixed Reed h h h h --

Dotsero Mixed Baker l l m l --

Gunnison

near Grand

Junction

Mixed Gunnison near

Grand Junction

m m m m --

Gunnison

Tunnel

Mixed

reference2

Lab cleaned -- -- -- -- --

Lab cleaned -- -- -- -- --

Lab cleaned -- -- -- -- --

East Rural urban,

recreation

Gunnison at

32 Road

l l mm

Gore Rural urban,

recreation

French l l l m h

French Mining French l l l m h

Dry Agriculture Lab cleaned -- -- -- -- --

Baker Reference,

srm3

Lab cleaned -- -- -- -- --

Lab cleaned -- -- -- -- --

1Concentration ranges with respect to all sites within the surface-water network, l = low, m = medium, h = high.

2Downstream from major reservoir system.

3Physiographic province, srm = Southern Rocky Mountain.
6 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

The difference in chloride values for the Gunnison

near Grand Junction site also is −0.1 mg/L (table 4),

but the percent difference is only −1.4. The lowest

rounding unit difference for both pairs of samples

is −1. The practical variability (measure of difference

between environmental and split-replicate samples due

to sample process, handling, shipping, and analysis) is

equivalent for both sets of samples.

Pre-Processing Split Replicates

Pre-processing split-replicate sampling for

general chemical constituents, nutrients, and trace

elements involves the collection of twice the normal

volume of water that is needed for a typical water

sample. The water is split into two samples—a typical

water-quality sample (termed the environmental

sample) and a pre-processing split-replicate sample.

Pre-processing split-replicate sampling for dissolved

and suspended organic carbon involves collecting

two separate samples (the environmental and

pre-processing split-replicate sample). Each sample

is then processed through all the normal steps of a

typical water-quality sample. For each step of sample

processing, the environmental sample is processed

first, and then the pre-processing split-replicate sample

is processed. The split-replicate sample is processed

using a new filter and clean equipment. Comparison

of results between the environmental samples and

the split-replicate samples provides an indication

of the variability associated with sample processing,

handling, shipment, and analysis. During water

years 1995–96, seven pairs of environmental and

split-replicate samples were collected. The distribution

of collection of the split-replicate samples by date and

site is shown in figure 2.

Comparison of General Chemical Constituents

Results of comparison of the environmental and

the pre-processing split-replicate samples for general

chemical constituents are listed in table 4. The differences between the environmental and split-replicate

values are given in the units of the constituent and in

units termed lowest rounding unit.

GUNNISON NEAR

GRAND JUNCTION

GORE

UNCOMPAHGRE

FRENCH

DRY

DRY FORK

BAKER

J F MA MJ J A SO S N N D D J FMAM A JJ O

DATE

SAMPLING SITES

1995 1996

Figure 2. Distribution of collection of pre-processing split-replicate samples, 1995–96.
QUALITY-CONTROL SAMPLING PROGRAM 7

Table 4. Comparison of environmental and pre-processing split-replicate samples for general chemical constituents[Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, mi

per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest roundi

the least significant figure]

Station Date

Calcium Magnesium Sodium 

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 E

(m

Gunnison near

Grand Junction

090596 120 120 0 0 33 33 0 0 53 53 0 0 3

Gore 102495 46 47 −1 −1 7.8 7.9 −0.1 −1 5.3 5.3 0 0 1

Uncompahgre 072596 86 90 −4 −4 10 10 0 0 17 17 0 0 1

French 090996 35 34 1 1 5.5 5.6 −0.1 −1 2 2 0 0 1 Dry 082996 170 170 0 0 36 37 −1 −1 47 47 0 0 2

Dry Fork 071596 83 83 0 0 130 130 0 0 300 310 −10 −1 2

Baker 071696 6.8 6.8 0 0 1.7 1.7 0 0 1.4 1.4 0 0 0Maximum difference −4 −4 −1 −1 −10 −1 Percent of samples with

no difference

57 57 57 57 86 86 

Percent of samples within

plus or minus 1 lowestrounding unit

86 100 100 

Station Date

Sulfate Chloride Fluoride 

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 E

(m

Gunnison near

 Grand Junction

090596 390 390 0 0 7.1 7.2 −0.1 −1 0.5 0.5 0 0 

Gore 102495 40 40 0 0 8.1 8 0.1 1 0.2 0.2 0 0 Uncompahgre 072596 170 170 0 0 3 3 0 0 0.5 0.5 0 0 French 090996 81 82 −1 −1 1 1.1 −0.1 −1 0.1 0.1 0 0 Dry 082996 450 450 0 0 5.9 6.1 −0.2 −2 0.9 0.9 0 0 2Dry Fork 071596 950 960 −10 −1 9.4 9.5 −0.1 −1 0.3 0.3 0 0 3

Baker 071696 4.1 4.2 −0.1 −1 0.1 0.1 0 0 0.3 0.2 0.1 1 

Maximum difference −10 −1 −0.2 −2 0.1 1 

Percent of samples with

no difference

57 57 29 29 86 86 

Percent of samples within

plus or minus 1 lowestrounding unit

100 86 100 
8 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

Table 4. Comparison of environmental and pre-processing split-replicate samples for general chemical constituents—Continued[Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, mill

per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding the least significant figure]

Station Date

Silica Iron 

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

(

Gunnison near

Grand Junction

090596 13 13 0 0 3 3 0 0 15 

Gore 102495 5.4 5.4 0 0 3 3 0 0 3 Uncompahgre 072596 10 10 0 0 3 3 0 0 46 

French 090996 9.5 9.4 0.1 1 11 15

−4 −4 10 

Dry 082996 20 19 1 1 3 3 0 0 67 Dry Fork 071596 16 16 0 0 9 9 0 0 4 Baker 071696 6.7 6.6 0.1 1 130 120 10 1 9 Maximum difference 1 1 10

−4 

Percent of samples with

no difference

57 57 71 71 

Percent of samples within

plus or minus 1 lowestrounding unit

100 86 

Station Date

Laboratory pH Laboratory specific conductance Res

Env. Split Diff. 1 Diff. 2 Env.

(μS/cm)

Split

(μS/cm)

Diff. 1

(μS/cm) Diff. 2 Env. (mg/L) 

(

(standard units)

Gunnison near

Grand Junction

090596 8.0 8.0 0 0 980 978 2 2 749 

Gore 102495 8.0 7.9 0.1 1 329 327 2 2 193 Uncompahgre 072596 8.0 8.0 0 0 575 573 2 2 396 French 090996 7.1 7.3

−0.2

−2 255 256

−1 −1 164 

Dry 082996 7.9 7.9 0 0 1,200 1,210

−10

−1 916 

Dry Fork 071596 8.1 8.1 0 0 2,290 2,290 0 0 1,730 1

Baker 071696 7.6 7.8

−0.2

−2 59 61

−2 −2 44 

Maximum difference

−0.2

−2 −10 2

Percent of samples with

no difference

57 57 14 14 

Percent of samples within

plus or minus 1 lowestrounding unit

71 43 
QUALITY-CONTROL SAMPLING PROGRAM 9

A summary of the differences for the constituents listed in table 4 is given in table 5. Except for

specific conductance and residue on evaporation,

most of the environmental and pre-processing splitreplicate samples agree within plus or minus 1 lowest

rounding unit. The differences for conductance agree

within plus or minus 2 lowest rounding units. These

differences would equal plus or minus 2 μS/cm

(microsiemens per centimeter at 25 degrees Celsius)

for all but the Dry sample (table 4) and probably are

well within instrument variation. Differences of

2 μS/cm are not considered excessive. Differences

between environmental and split-replicate samples for

residue on evaporation are greater than any other of

the constituent differences. It appears that differences

of a few lowest rounding units for residue on evaporation would be common, and lower differences may

be limited by the precision of the laboratory method.

Results in table 4 that have differences greater than

plus or minus 1 lowest rounding unit have been

shaded. By observation of the random position of

the shaded cells, it appears that the larger differences

for each constituent do not seem to be related to the

concentration or the sampling site. Variability associated with sample processing, handling, shipment,

and analysis for general chemical constituents is low

and will have little effect on interpretation of environmental data.

Comparison of Nutrients and Organic Carbon

Results of comparison of the environmental

and pre-processing split-replicate samples for nutrients, dissolved organic carbon, and suspended organic

carbon are listed in table 6. To determine the differences between the environmental and pre-processing

split-replicate sample concentrations for values less

than the laboratory reporting limit (values that

have a less-than symbol), a value of one-half of the

reporting limit was substituted for the less-than value.

A summary of the differences between environmental

and pre-processing split-replicate samples for each

constituent is listed in table 7. Most of the differences

between the environmental and pre-processing splitreplicate samples for all constituents are within plus

or minus 1 lowest rounding unit. Variability associated

with sample processing, handling, shipment, and

analysis for nutrients and organic carbon is low and

will have little effect on interpretation of environmental data.

Table 5. Summary of differences between environmental and pre-processing split-replicate samples for general chemical

constituents

[Lowest rounding unit is equal to the magnitude of the least significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding units

Calcium 57 86 86

Magnesium 57 100 100

Sodium 86 100 100

Potassium 29 86 100

Sulfate 57 100 100

Chloride 29 86 100

Fluoride 86 100 100

Laboratory alkalinity 71 71 86

Silica 57 100 100

Iron 71 86 86

Manganese 71 86 86

Laboratory pH 57 71 100

Laboratory specific conductance 14 43 100

Residue on evaporation 14 14 28
10 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

Table 6. Comparisons of environmental and pre-processing split-replicate samples for nutrients and organic carbon[Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, millrepresent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to magnitude of the least significant figure; <, value is less than the llevel]

Station Date

Ammonia Dissolved ammonia plus organic Total am

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) S

(m

Gunnison near

Grand Junction

090596 0.02 0.02 0 0 0.3 0.2 0.1 1 0.4 0

Gore 102495 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <0Uncompahgre 072596 0.03 0.03 0 0 <0.2 <0.2 0 0 0.3 0French 090996 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <0Dry 082996 0.05 0.05 0 0 0.4 0.4 0 0 0.8 0Dry Fork 071596 0.03 0.02 0.01 1 0.3 0.2 0.1 1 0.3 0Baker 071696 0.04 0.02 0.02 2 <0.2 <0.2 0 0 <0.2 <0Maximum difference 0.02 2 0.1 1

Percent of samples with

no difference

71 71 71 71 

Percent of samples

within plus or minus 1lowest rounding unit

86 100 

Station Date

Nitrite Nitrite plus nitrate Dissolved organic carbon S

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 En

(mg

Gunnison near

Grand Junction

090596 0.01 0.02

−0.01

−1 1.5 1.5 0 0 3.5 3.4 0.1 1 0

Gore 102495 <0.01 <0.01 0 0 0.44 0.44 0 0 1.4 1.3 0.1 1 0

Uncompahgre 072596 0.01 0.01 0 0 0.14 0.14 0 0 1 0.9 0.1 1 0French 090996 <0.01 <0.01 0 0 0.07 0.08

−0.01

−1 0.5 0.4 0.1 1 <0

Dry 082996 0.02 0.02 0 0 3.9 3.9 0 0 3.4 3.5

−0.1

−1 2

Dry Fork 071596 0.01 0.01 0 0 0.79 0.8

−0.01

−1 5.2 5.1 0.1 1 0

Baker 071696 0.01 0.01 0 0 0.1 0.09 0.01 1 1.9 1.9 0 0 0

Maximum difference

−0.01

−1 0.01 1 1 1 

Percent of samples with

no difference

86 86 57 57 14 14 

Percent of samples

within plus or minus 1lowest rounding unit

100 100 100 
QUALITY-CONTROL SAMPLING PROGRAM 11

Table 6. Comparisons of environmental and pre-processing split-replicate samples for nutrients and organic carbon—Continued[Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milrepresent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to magnitude of the least significant figure; <, value is less than the 

level]

Station Date

Dissolved phosphorus Total phosphorus Or

Env.

(mg/L)

Split

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Split (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) S

(m

Gunnison near

Grand Junction

090596 0.04 <0.01 0.035 3.5 0.05 0.05 0 0 <0.01 <0

Gore 102495 0.03 0.03 0 0 0.04 0.04 0 0 0.04 0Uncompahgre 072596 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 <0French 090996 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 <0Dry 082996 0.02 0.02 0 0 0.18 0.19 −0.01 −1 0.03 0Dry Fork 071596 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 0Baker 071696 <0.01 <0.01 0 0 <0.01 0.03 −0.025 2.5 <0.01 <0Maximum difference 0.035 3.5 −0.025 −2.5 Percent of samples with

no difference

86 86 71 71 

Percent of samples

within plus or minus1 lowest roundingunit

86 86 
12 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

Comparison of Trace Elements

Trace-element samples are routinely collected

at only two of the network sites, therefore only two

pre-processing split replicates were collected for

trace-element constituents. The environmental and

pre-processing split-replicate results for these samples

are listed in table 8. Because of the low number

of pairs of samples, percentage of samples within

ranges of rounding units are not provided. Many

of the trace-element concentrations are less than the

laboratory reporting limit (indicated by a less-than

value). To determine the differences between the

environmental and pre-processing split-replicate

sample concentrations, a value of one-half of the

reporting limit was substituted for the values designated as a “less than.” None of the differences were

greater than 1 ug/L (microgram per liter) or 1 lowest

rounding unit.

Table 7. Summary of differences between environmental and pre-processing split-replicate samples for nutrients and

organic carbon

[Lowest rounding unit is equal to the magnitude of the least significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding units

Ammonia 71 86 100

Dissolved ammonia plus organic 71 100 100

Total ammonia plus organic 57 86 86

Nitrite 86 100 100

Nitrite plus nitrate 57 100 100

Dissolved organic carbon 14 100 100

Suspended organic carbon 29 71 71

Dissolved phosphorus 86 86 86

Total phosphorus 71 86 86

Orthophosphate 100 100 100
QUALITY-CONTROL SAMPLING PROGRAM 13

Table 8. Comparison of environmental and pre-processing split-replicate samples for trace elements[Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; lowest magnitude of the least significant figure; μg/L, micrograms per liter; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; <, value is l

reporting level]

Station Date

Arsenic Aluminum Antimony 

Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env. (μg/L) Split (μg/L) Diff. 1 (μg/L) Diff. 2 Env. (μg/L) Split (μg/L) Diff. 1 (μg/L) Diff. 2 Env. (μg/L) 

Uncompahgre 072596 2 2 0 0 50 50 0 0 <1 <1 0 0 41 French 090996 <1 <1 0 0 5 4 1 1 <1 <1 0 0 23 Maximum difference 0 0 1 1 0 0 Number of samples with

no difference

22 11 22 

Number of samples

within plus or minus 1lowest rounding unit

222

Station Date

Beryllium Cadmium Chromium 

Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env. (μg/L) Split (μg/L) Diff. 1 (μg/L) Diff. 2 Env. (μg/L) Split (μg/L) Diff. 1 (μg/L) Diff. 2 Env. (μg/L) 

Uncompahgre 072596 <1 <1 0 0 1 1 0 0 1 <1 0.5 0.5 <1 French 090996 <1 <1 0 0 7 7 0 0 <1 <1 0 0 <1 Maximum difference 0 0 0 0 0.5 0.5 Number of samples with

no difference

22 22 1 1 

Number of samples

within plus or minus 1lowest rounding unit

222
14 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96 Table 8. Comparison of environmental and pre-processing split-replicate samples for trace elements—Continued [Env., environmental sample; Split, pre-processing split-replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; lowest 

magnitude of the least significant figure; μg/L, micrograms per liter; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; <, value is reporting level] Station Date Copper Lead Molybdenum 

Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Uncompahgre 072596 3 4

−1 −1 <1 <1 0 0 2 2 0 0 2 

French 090996 1 1 0 0 5 4 1 1 <1 <1 0 0 2 Maximum difference

−1 −1 11 00

Number of samples with

no difference

11 11 22 

Number of samples

within plus or minus 1lowest rounding unit

22 2 

Station Date

Selenium Silver Uranium 

Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Split

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Uncompahgre 072596 <1 <1 0 0 <1 <1 0 0 <1 <1 0 0 14 French 090996 <1 <1 0 0 <1 <1 0 0 <1 <1 0 0 2,400 Maximum difference 0 0 0 0 0 0 Number of samples with

no difference

2 2 22 2 2 

Number of samples

within plus or minus 1lowest rounding unit

22 2
QUALITY-CONTROL SAMPLING PROGRAM 15

Concurrent and Sequential Replicates

Concurrent and sequential replicates differ

from the split replicates in that two separate samples

are collected from the river. In the concurrent replicate, one sample is collected concurrently with the

environmental sample using a second collection

team or second set of collection equipment. In the

sequential replicate, a replicate is collected as close

in time as possible to the environmental sample. Each

sample is processed through all the normal steps of a

typical water-quality sample. For each step of sample

processing, the environmental sample is processed

first, and then the replicate sample is processed. The

replicate samples are processed using a clean filter

and equipment. The concurrent and sequential replicates include all the potential sources for variation

as with the pre-processing split replicates as well

as the variation due to sample-collection technique

and short-term environmental variations in the river.

The distribution of collection of the concurrent and

sequential replicates by site and date is shown in figure

3.

Seven concurrent- and three sequentialreplicate samples were collected during water

years 1995–96. The comparison of environmental

and concurrent-replicate samples and environmental

and sequential-replicate samples for general chemical,

nutrient, and organic carbon constituents is presented

in the following sections. Concurrent- and sequentialreplicate data for trace elements are not presented

because only one concurrent and no sequential replicates for trace elements were collected.

Comparison of General Chemical Constituents

Results of comparison between environmental

and concurrent-replicate samples and between environmental and sequential-replicate samples for general

chemical constituents are listed in table 9. A summary

of the differences between the environmental and the

concurrent-replicate samples for the constituents listed

in table 9 is given in table 10. The sequential-replicate

comparisons are not summarized because only three

samples are available. The majority of the differences

agree within plus or minus 1 lowest rounding unit with

the exception of laboratory specific conductance and

residue on evaporation. The majority of the conductance differences agree within plus or minus 2 lowest

rounding units. One-half of the differences for residue

on evaporation are within plus or minus 2 lowest

rounding units and probably indicate the precision of

the laboratory method. Shaded cells in table 9 represent differences greater than plus or minus 1 lowest

CAMEO

STATE LINE

DOTSERO

GUNNISON

AT 32 ROAD

EAST

GORE

REED

BAKER

DATE

SAMPLING SITES

1995 1996

CONCURRENT REPLICATES

SEQUENTIAL REPLICATES

J FMA M J J AS O S N N D D J FM AM A JJ O

Figure 3. Distribution of collection of concurrent- and sequential-replicate samples, 1995–96.
16 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96 Table 9. Comparison of environmental and concurrent- and sequential-replicate samples for general chemical constituents [Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; μ

cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure; μS/cm, mi

degrees Celsius] Station Date Calcium Magnesium Sodium 

Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L

Concurrent replicates State Line 091096 120 120 0 0 35 35 0 0 90 92

−2 −2 4.2 

Cameo 051396 34 33 1 1 7.2 7.1 0.1 1 20 20 0 0 1.4 

Gunnison at 32 Road 071895 22 22 0 0 4.5 4.5 0 0 2.4 2.4 0 0 0.8 East 113095 46 47

−1 −1 8.5 8.6

−0.1

−1 4.3 4.3 0 0 0.9 

East 051696 22 23

−1 −1 3.5 3.7

−0.2

−2 1.4 1.5

−0.1

−1 0.6 

Gore 082396 42 41 1 1 7.3 7.2 0.1 1 4.7 4.5 0.2 2 1.1 Baker 081895 7.4 7.5

−0.1

−1 1.8 1.8 0 0 1.4 1.4 0 0 0.8 

Maximum difference 1 1

−0.2 2

−2 −2 

Percent of samples with

no difference

29 29 43 43 57 57 

Percent of samples

within plus or minus 1lowest rounding unit

100 86 71 

Sequential Replicates

Dotsero 032096 39 39 0 0 7.7 7.7 0 0 17 17 0 0 1.8 Reed 112295 550 540 10 1 220 210 10 1 300 290 10 1 9.5 Baker 022796 9.1 9.0 0.1 1 2.4 2.4 0 0 1.9 1.9 0 0 0.9 Maximum difference 10 1 10 1 10 1 Number of samples with

no difference

11 22 2 2 

Number of samples

within plus or minus 1lowest rounding unit

333
QUALITY-CONTROL SAMPLING PROGRAM 17

Table 9. Comparison of environmental and concurrent- and sequential-replicate samples for general chemical constituents—Continu[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; μ

shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure; μS/c

at 25 degrees Celsius]

Station Date

Sulfate Chloride Fluoride L

Env.

(mg/L)

Rep.

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L

Concurrent replicates

State Line 091096 370 370 0 0 80 84 −4 −4 0.4 0.4 0 0 169 Cameo 051396 40 40 0 0 22 22 0 0 0.2 0.2 0 0 89 Gunnison at 32 Road 071895 8.3 8.4 −0.1 −1 1 0.6 0.4 4 0.1 0.1 0 0 70 East 113095 34 34 0 0 1.2 1.1 0.1 1 0.2 0.1 0.1 1 125 East 051696 9.9 10 −0.1 −1 0.4 0.5 −0.1 −1 0.1 0.1 0 0 64 

Gore 082396 35 35 0 0 5.7 5.5 0.2 2 0.1 0.1 0 0 103 Baker 081895 4.9 4.9 0 0 0.2 0.1 0.1 1 0.3 0.3 0 0 26 Maximum difference −0.1 −1 −4 4 0.1 1 Percent of samples with

no difference

71 71 14 14 86 86 

Percent of samples

within plus or minus 1lowest rounding unit

100 57 100 

Sequential replicates

Dotsero 032096 65 62 3 3 21 20 1 1 0.3 0.3 0 0 80 Reed 112295 2,200 2,200 0 0 200 200 0 0 0.3 0.1 0.2 2 302 Baker 022796 6.5 6.5 0 0 0.1 0.1 0 0 0.3 0.3 0 0 32 Maximum difference 3 3 1 1 0.2 2 Number of samples with

no difference

22 22 22 

Number of samples

within plus or minus 1lowest rounding unit

232
18 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96 Table 9. Comparison of environmental and concurrent- and sequential-replicate samples for general chemical constituents

—Continue

[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; μshaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure; μS/cm

at 25 degrees Celsius]

Station Date

Silica Iron M

Env.

(mg/L)

Rep.

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env.

(μg/L)

Rep.

(μg/L)

Diff. 1

(μg/L) Diff. 2 Env.

(μg/L)

Re

(μg

Concurrent replicates

State Line 091096 12 12 0 0 3300 21Cameo 051396 8.6 8.7

−0.1

−1 24 84

−60

−60 16 17

Gunnison at 32 Road 071895 9.1 9.1 0 0 73 71 2 2 21 21 East 113095 6.7 6.8

−0.1

−1 3300 33

East 051696 5.1 5.4

−0.3

−3 25 25 0 0 10 10 

Gore 082396 5.2 5.1 0.1 1 5411 22

Baker 081895 6.9 6.9 0 0 190 200

−10

−1 12 12 

Maximum difference

−0.3

−3 −60

−60 

Percent of samples with

no difference

43 43 43 43 

Percent of samples

within plus or minus 1lowest rounding unit

86 71 

Sequential replicates

Dotsero 032096 7.8 8

−0.2

−2 13 12 1 1 21 21 

Reed 112295 10 10 0 0 9 11

−2 −2 100 100 

Baker 022796 9.4 9.3 0.1 1 130 150

−20

−2 37 37 

Maximum difference

−0.2

−2 −20

−2 

Number of samples with

no difference

1 1 00 

Number of samples

within plus or minus 1lowest rounding unit

21
QUALITY-CONTROL SAMPLING PROGRAM 19

Table 9. Comparison of environmental and concurrent- and sequential-replicate samples for general chemical constituents—Continu[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; 

shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure; μS/

at 25 degrees Celsius]

Station Date

Laboratory pH Laboratory specific conductance Residue 

Env. Rep. Diff. 1 Diff. 2 Env. (μS/cm) Rep. (μS/cm) Diff. 1 (μS/cm) Diff. 2 Env. (mg/L) Rep

(mg/L

(standard units)

Concurrent replicates

State Line 091096 8.1 8.1 0 0 1,230 1,230 0 0 852 846 Cameo 051396 7.8 7.9 −0.1 −1 334 332 2 2 203 210 

Gunnison at 32 Road 071895 7.8 7.8 0 0 159 157 2 2 97 94 East 113095 7.8 7.7 0.1 1 317 316 1 1 180 179 East 051696 7.8 7.8 0 0 152 153 −1 −1 92 -- 

Gore 082396 8.0 8.0 0 0 296 293 3 3 167 169 

Baker 081895 7.9 7.2 0.7 7 64 53 11 11 38 38 Maximum difference 0.7 7 11 11 

Percent of samples with

no difference

57 57 14 14 

Percent of samples

within plus or minus 1lowest rounding unit

86 43 

Sequential replicates

Dotsero 032096 7.7 7.9 −0.2 −2 366 355 11 11 222 213 Reed 112295 7.5 7.5 0 0 4,300 4,270 30 3 3,960 3,960 Baker 022796 7.4 7.3 0.1 1 81 81 0 0 48 50 

Maximum difference −0.2 −2 30 11 Number of samples with

no difference

11 1 1 

Number of samples

within plus or minus 1lowest rounding unit

21 
20 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

rounding unit. It does not appear that the larger differences are related to sampling site or constituent

concentration. Variability associated with sample

collection, processing, handling, shipment, and analysis for general chemical constituents is low and will

have little effect on interpretation of environmental

data.

Comparison of Nutrients and Organic Carbon

Results of comparison between environmental

and concurrent replicates and between environmental

and sequential replicates for nutrients, dissolved

organic carbon, and suspended organic carbon are

listed in table 11. Shaded cells in table 11 represent

differences greater than plus or minus 1 lowest

rounding unit. The pattern of shaded cells indicates

that the larger differences are not related to sampling

site or constituent concentration. A summary of

the differences between the environmental and

concurrent-replicate samples for the constituents in

table 11 is given in table 12. Sequential-replicate

differences are not summarized because of the

small number of samples available. The majority of

the differences are within plus or minus 1 lowest

rounding unit with the exception of suspended organic

carbon. The majority of the suspended organic

carbon differences are within plus or minus 2 lowest

rounding units. Variability associated with sample

collection, processing, handling, shipment, and analysis for nutrients and organic carbon is low and will

have little effect on interpretation of environmental

data.

Table 10. Summary of differences between environmental and concurrent-replicate samples for general chemical

constituents

[Lowest rounding unit is equal to the magnitude of the least significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding units

Calcium 29 100 100

Magnesium 43 86 100

Sodium 57 71 100

Potassium 57 100 100

Sulfate 71 100 100

Chloride 14 57 71

Fluoride 86 100 100

Laboratory alkalinity 43 71 86

Silica 43 86 86

Iron 43 71 86

Manganese 71 100 100

Lab pH 57 86 86

Laboratory specific conductance 14 43 71

Residue on evaporation 17 34 50
QUALITY-CONTROL SAMPLING PROGRAM 21

Table 11. Comparison of environmental and concurrent- and sequential-replicate samples for nutrients and organic carbon[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; <, minimum reporting level; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the leas

Station Date

Ammonia Dissolved ammonia plus organic Total am

Env.

(mg/L)

Rep.

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Re

(mg

Concurrent replicates

State Line 091096 0.07 0.08 −0.01 −1 0.3 0.3 0 0 0.8 Cameo 051396 <0.02 <0.02 0 0 <0.2 0.2 −0.1 −1 1.2 

Gunnison at 32 Road 071895 0.02 0.02 0 0 <0.2 <0.2 0 0 <0.2 <East 113095 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <East 051696 0.02 0.02 0 0 <0.2 <0.2 0 0 0.3 Gore 082396 0.02 0.02 0 0 <0.2 <0.2 0 0 <0.2 <Baker 081895 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <Maximum difference −0.01 −1 −0.1 −1 

Percent of samples with

no difference

86 86 86 86 

Percent of samples

within plus or minus 1lowest rounding unit

100 100 

Sequential replicates

Dotsero 032096 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 

Reed 112295 0.06 0.06 0 0 0.4 0.4 0 0 0.5 Baker 022796 0.02 <0.02 0.01 1 <0.2 <0.2 0 0 <0.2 <Maximum difference 0.01 1 0 0 

Number of samples with

no difference

2 2 3 3 

Number of samples

within plus or minus 1lowest rounding unit

3 3
22 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96 Table 11. Comparison of environmental and concurrent- and sequential-replicate samples for nutrients and organic carbon

—Continued

[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; <, vminimum reporting level; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least 

Station Date

Nitrite Nitrite plus nitrate Dissolved organic carbon S

Env.

(mg/L)

Rep.

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 En

(mg

Concurrent replicates

State Line 091096 0.02 0.02 0 0 1 1 0 0 3.3 3.9

−0.6

−6 3

Cameo 051396 <0.01 <0.01 0 0 0.14 0.14 0 0 4 4 0 0 3

Gunnison at 32 Road 071895 <0.01 <0.01 0 0 <0.05 <0.05 0 0 2.5 2.6

−0.1

−1 0

East 113095 <0.01 <0.01 0 0 0.08 0.11

−0.03

−3 0.6 0.8

−0.2

−2 0

East 051696 <0.01 <0.01 0 0 0.12 0.14

−0.02

−2 2.6 3

−0.4

−4 0

Gore 082396 <0.01 <0.01 0 0 0.48 0.48 0 0 1.1 1.1 0 0 0Baker 081895 <0.01 <0.01 0 0 <0.05 <0.05 0 0 1.5 1.5 0 0 0Maximum difference 0 0

−0.3

−3 −0.6

−6 

Percent of samples with

no difference

100 100 71 71 43 43 

Percent of samples

within plus or minus 1lowest rounding unit

100 71 57 

Sequential replicates

Dotsero 032096 <0.01 <0.01 0 0 0.13 0.12 0.01 1 2.5 2.2 0.3 3 0Reed 112295 0.05 0.05 0 0 8.3 8.3 0 0 4.8 4.7 0.1 1 0Baker 022796 <0.01 <0.01 0 0 0.11 0.10 0.01 1 1.0 1.1

−0.1

−1 0

Maximum difference 0 0 0.01 1 0.3 3 Number of samples with

no difference

33 1 1 0 0 

Number of samples

within plus or minus 1lowest rounding unit

332
QUALITY-CONTROL SAMPLING PROGRAM 23

Table 11. Comparison of environmental and concurrent- and sequential-replicate samples for nutrients and organic carbon—Continued[Env., environmental sample; Rep., replicate sample; Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; <, vminimum reporting level; shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least 

Station Date

Dissolved phosphorus Total phosphorus O

Env.

(mg/L)

Rep.

(mg/L)

Diff. 1

(mg/L) Diff. 2 Env. (mg/L) Rep. (mg/L) Diff. 1 (mg/L) Diff. 2 Env. (mg/L) R

(m

Concurrent replicates

State Line 091096 0.01 0.01 0 0 0.21 0.23 −0.02 −2 0.02 0

Cameo 051396 <0.01 0.03 −0.025 −2.5 0.54 0.44 0.10 10 <0.01 <0

Gunnison at 32 Road 071895 <0.01 <0.01 0 0 0.01 0.02 −0.01 −1 0.01 0

East 113095 0.01 <0.01 0.005 0.5 <0.01 <0.01 0 0 <0.01 <0East 051696 0.01 0.01 0 0 0.06 0.05 0.01 1 <0.01 <0Gore 082396 0.04 0.04 0 0 0.08 0.05 0.03 3 0.05 0Baker 081895 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 <0Maximum difference −0.025 −2.5 0.10 10 

Percent of samples with

no difference

71 71 29 29 

Percent of samples

within plus or minus 1lowest rounding unit

86 57 

Sequential replicates

Dotsero 032096 <0.01 <0.01 0 0 0.03 0.05 −0.02 −2 0.01 0

Reed 112295 <0.01 <0.01 0 0 0.03 0.01 0.02 2 <0.01 <0Baker 022796 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 <0Maximum difference 0 0 0.02 2 Number of samples with

no difference

3 3 1 1 

Number of samples

within plus or minus 1lowest rounding unit

3 1
24 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

Post-Processing Split Replicates

A post-processing split replicate is a

processed sample that is poured into identical

bottles and thus split into two separate samples (split

A

and split B). Split A and split B are submitted to

the laboratory for analysis as unique samples.

These pairs of samples help to evaluate the potential

sources of variability resulting from sample

shipping and analysis. Variability resulting from

sample collection and processing is not evaluated

by post-processing split-replicate sampling. The

distribution of collection of the post-processing

Table 12. Summary of differences between environmental and concurrent-replicate samples for nutrients and organic carbon

[Lowest rounding unit is equal to the magnitude of the least significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding units

Ammonia 86 100 100

Dissolved ammonia plus organic 86 100 100

Total ammonia plus organic 86 86 86

Nitrite 100 100 100

Nitrite plus nitrate 71 71 86

Dissolved organic carbon 43 57 71

Suspended organic carbon 43 43 71

Dissolved phosphorus 71 86 86

Total phosphorus 29 57 71

Orthophosphate 100 100 100
QUALITY-CONTROL SAMPLING PROGRAM 25

split-replicate samples by site and date is shown in

figure 4.

Eight post-processing split-replicate samples

were collected during water years 1995–96.

Comparisons of split A and split B samples

for major chemical, nutrient, and organic carbon

constituents are presented in the following sections.

Post-processing split-replicate data for trace

elements are not presented because only one

sample for trace elements was collected.

Comparison of General Chemical Constituents

Results of comparison between post-processing

split samples for general chemical constituents are

listed in table 13. A summary of the differences

between split A and split B samples for the constituents listed in table 13 is given in table 14. Shaded

cells in table 13 represent differences greater than

plus or minus 1 rounding unit. The majority of the

differences agree within plus or minus 1 lowest

rounding unit with the exception of residue on evaporation. The differences in residue on evaporation

probably reflect the precision of the laboratory

method. Variability associated with sample shipment

CAMEO

STATE LINE

GUNNISON

TUNNEL

GUNNISON

AT 32 ROAD

EAST

GORE

BAKER

DATE

SAMPLING SITES

1995 1996

J FMA MJ JAS O S N N D D J FMAM A JJ O

Figure 4. Distribution of collection of post-processing split-replicate samples, 1995–96.
26 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

Table 13. Comparison of post-processing split-replicate samples for general chemical constituents[Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per ce

shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure]

Station Date

Calcium Magnesium Sodium 

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Spl

(mg

State Line 091096 120 120 0 0 35 35 0 0 92 92 0 0 4

Cameo 051396 33 33 0 0 7.1 7.2

−0.1

−1 20 20 0 0 1

Gunnison Tunnel 062995 18 17 1 1 3.7 3.6 0.1 1 3.9 3.8 0.1 1 1Gunnison at 32 Road 071895 22 22 0 0 4.5 4.5 0 0 2.4 2.3 0.1 1 0East 113095 47 46 1 1 8.6 8.5 0.1 1 4.3 4.3 0 0 0East 051696 23 23 0 0 3.7 3.7 0 0 1.5 1.5 0 0 0Gore 082396 41 41 0 0 7.2 7.2 0 0 4.5 4.5 0 0 1Baker 081895 7.5 7.5 0 0 1.8 1.8 0 0 1.4 1.4 0 0 0Maximum difference 1 1 0.1 1 0.1 1

Percent of samples with

no difference

75 75 62 62 75 75 

Percent of samples

within plus or minus 1lowest rounding unit

100 100 100 

Station Date

Sulfate Chloride Fluoride 

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Spl

(mg

State Line 091096 370 370 0 0 84 78 6 6 0.4 0.4 0 0 18Cameo 051396 40 40 0 0 22 22 0 0 0.2 0.2 0 0 87 Gunnison Tunnel 062995 13 13 0 0 0.7 0.7 0 0 0.1 0.1 0 0 5Gunnison at 32 Road 071895 8.4 8.4 0 0 0.6 0.6 0 0 0.1 0.1 0 0 7East 113095 34 34 0 0 1.1 1.2

−0.1

−1 0.1 0.2

−0.1

−1 12

East 051696 10 10 0 0 0.5 0.5 0 0 0.1 0.1 0 0 64 Gore 082396 35 35 0 0 5.5 5.5 0 0 0.1 0.1 0 0 10Baker 081895 4.9 5

−0.1

−1 0.1 0.1 0 0 0.3 0.2 0.1 1 2

Maximum difference

−0.1

−1 6 6 0.1 1 

Percent of samples with

no difference

88 88 75 75 75 75 

Percent of samples

within plus or minus 1lowest rounding unit

100 88 100 
QUALITY-CONTROL SAMPLING PROGRAM 27

Table 13. Comparison of post-processing split-replicate samples for general chemical constituents—Continued[Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per 

shaded cells represent differences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to the magnitude of the least significant figure]

Station Date

Silica Iron M

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (μg/L) Split B (μg/L) Diff. 1 (μg/L) Diff. 2 Split A (μg/L) Spl

(μg

State Line 091096 12 12 0 0 3 3 0 0 1 Cameo 051396 8.7 8.7 0 0 84 83 1 1 17 17 Gunnison Tunnel 062995 16 16 0 0 52 49 3 3 3 3 Gunnison at 32 Road 071895 9.1 9.2 −0.1 −1 71 72 −1 −1 21 2

East 113095 6.8 6.7 0.1 1 3 3 0 0 3 3 East 051696 5.4 5.4 0 0 25 23 2 2 10 10 Gore 082396 5.1 5.1 0 0 4 5 −1 −1 22 

Baker 081895 6.9 6.9 0 0 200 190 10 1 12 12 Maximum difference 0.1 1 10 3 Percent of samples with

no difference

75 75 25 25 

Percent of samples

within plus or minus 1lowest rounding unit

100 75 

Station Date

Laboratory pH Laboratory specific conductance Residu

Split A Split B Diff. 1 Diff. 2 Split A

μS/cm

Split B

μS/cm

Diff. 1

μS/cm Diff. 2 Split A Spl

(standard units) (mg/L) (mg

State Line 091096 8.1 8.1 0 0 1,230 1,230 0 0 846 86

Cameo 051396 7.9 7.8 0.1 1 332 332 0 0 210 21Gunnison Tunnel 062995 7.1 7.6 −0.5 −5 141 142 −1 −1 90 8

Gunnison at 32 Road 071895 7.8 7.9 −0.1 −1 157 157 0 0 94 8

East 113095 7.7 7.6 0.1 1 316 317 −1 −1 179 17

East 051696 7.8 7.7 0.1 1 153 151 2 2 -- 8Gore 082396 8.0 8.1 −0.1 −1 293 294 −1 −1 169 16

Baker 081895 7.2 7.3 −0.1 −1 53 64 −11 −11 38 3

Maximum difference −0.5 −5 −11 −11 

Percent of samples with

no difference

12 12 38 38 

Percent of samples

within plus or minus 1lowest rounding unit

88 75 
28 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

and analysis for general chemical constituents is low

and will have little effect on interpretation of environmental data.

Comparison of Nutrients and Organic Carbon

Results of comparison between post-processing

split-replicate samples for nutrients and dissolved

organic carbon are listed in table 15. Suspended

organic carbon is not included. The analysis of

suspended organic carbon uses all the sediment on the

filter paper. These splits are obtained after processing

has been completed, and splitting the filter paper for

analysis would not be an acceptable method. A value

of one-half the reporting limit was substituted for

values less than the reporting limit (values with a

less than) to determine the differences between the

post-processing split-replicate samples. Shaded cells

in table 15 represent differences greater than plus or

minus 1 rounding unit. The pattern of shaded cells

indicates that the larger differences are not related to

sampling site or constituent concentration. A summary

of the differences between the post-processing splitreplicate samples for the constituents in table 15 is

given in table 16. The majority of the differences

agree within plus or minus 1 lowest rounding unit.

Table 14. Summary of differences between post-processing split-replicate samples for general chemical constituents

[Lowest rounding unit is equal to the magnitude of the least significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding units

Calcium 75 100 100

Magnesium 62 100 100

Sodium 75 100 100

Potassium 88 100 100

Sulfate 88 100 100

Chloride 75 88 88

Fluoride 75 100 100

Laboratory alkalinity 100 100 100

Silica 75 100 100

Iron 25 75 88

Manganese 100 100 100

Laboratory pH 12 88 88

Laboratory specific conductance 38 75 88

Residue on evaporation 29 29 43
QUALITY-CONTROL SAMPLING PROGRAM 29

Table 15. Comparison of post-processing split-replicate samples for nutrients and organic carbon[Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; <, value is less than the laboratory minimum reporting ledifferences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to magnitude of the least significant figure; --, no data]

Station Date

Ammonia Dissolved ammonia plus organic Total am

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Split A (mg/L) Sp

(m

State Line 091096 0.08 0.08 0 0 0.3 0.3 0 0 0.8 Cameo 051396 <0.02 <0.02 0 0 <0.2 <0.2 0 0 1.5 Gunnison Tunnel 062995 <0.02 <0.02 0 0 <0.2 <0.2 0 0 0.2 <Gunnison at 32 Road 071895 0.02 0.02 0 0 <0.2 <0.2 0 0 <0.2 <East 113095 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <East 051696 0.02 0.02 0 0 <0.2 <0.2 0 0 0.3 Gore 082396 0.02 0.02 0 0 <0.2 <0.2 0 0 <0.2 <Baker 081895 <0.02 <0.02 0 0 <0.2 <0.2 0 0 <0.2 <Maximum difference 0 0 0 0 Percent of samples with

no difference

100 100 100 100 

Percent of samples

within plus or minus 1lowest rounding unit

100 100 

Station Date

Nitrite Nitrite plus nitrate Dissol

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Split A (mg/L) Sp

(m

State Line 091096 0.02 0.02 0 0 1.00 0.97 0.03 3 3.9 3Cameo 051396 <0.01 <0.01 0 0 0.14 0.13 0.01 1 4 4 Gunnison Tunnel 062995 <0.01 <0.01 0 0 <0.05 <0.05 0 0 3.4 3Gunnison at 32 Road 071895 <0.01 <0.01 0 0 <0.05 <0.05 0 0 2.6 2East 113095 <0.01 <0.01 0 0 0.11 0.08 0.03 3 0.8 0East 051696 <0.01 <0.01 0 0 0.14 0.12 0.02 2 3 Gore 082396 <0.01 <0.01 0 0 0.48 0.47 0.01 1 1.1 

Baker 081895 <0.01 <0.01 0 0 <0.05 <0.05 0 0 1.5 Maximum difference 0 0 0.03 3 Percent of samples with

no difference

100 100 38 38 

Percent of samples

within plus or minus 1lowest rounding unit

100 62 
30 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96 Table 15. Comparison of post-processing split-replicate samples for nutrients and organic carbon

—Continued

[Diff. 1, difference in units of constituent; Diff. 2, difference in lowest rounding unit; mg/L, milligrams per liter; <, value is less than the laboratory minimum reporting ledifferences greater than plus or minus 1 lowest rounding unit; lowest rounding unit is equal to magnitude of the least significant figure; --, no data]

Station Date

Dissolved phosphorus Total phosphorus O

Split A

(mg/L)

Split B

(mg/L)

Diff. 1

(mg/L) Diff. 2 Split A (mg/L) Split B (mg/L) Diff. 1 (mg/L) Diff. 2 Split A (mg/L) Sp

(m

State Line 091096 0.01 0.01 0 0 0.23 0.20 0.03 3 0.02 0Cameo 051396 0.03 0.01 0.02 2 0.44 0.31 0.13 13 <0.01 <0Gunnison Tunnel 062995 <0.01 <0.01 0 0 0.05 0.04 0.01 1 <0.01 <0Gunnison at 32 Road 071895 <0.01 0.01

−0.005

−0.5 0.02 0.01 0.01 1 0.01 0

East 113095 <0.01 0.01

−0.005

−0.5 <0.01 <0.01 0 0 <0.01 <0

East 051696 0.01 0.01 0 0 0.05 0.04 0.01 1 <0.01 <0Gore 082396 0.04 0.06

−0.02

−2 0.05 0.07

−0.02

−2 0.05 0

Baker 081895 <0.01 <0.01 0 0 <0.01 <0.01 0 0 <0.01 <0Maximum difference 0.02 2 0.13 13

Percent of samples with

no difference

50 50 25 25 

Percent of samples

within plus or minus 1lowest rounding unit

75 62 
QUALITY-CONTROL SAMPLING PROGRAM 31

Variability associated with sample shipment and

analysis for nutrients and organic carbon is low and

will have little effect on interpretation of environmental data.

Field Blanks

A field blank is a sample prepared using water

that is free of the analytes of interest. The blank water

is passed through all sampling equipment and then

processed as a typical water-quality sample. Results of

analysis of field blanks are used to test for bias that

could result from the contamination of environmental

samples as a result of sample collection, processing,

handling, shipping, and analysis. Specifically, field

blanks demonstrate that equipment has been properly

cleaned to remove contamination from other samples,

that sample collection and processing do not contaminate samples, and that sample handling, transport,

and analysis have not contaminated the sample.

Twelve field-blank samples were collected during

water years 1995–96. The distribution of collection

of field-blank samples by site and date is shown in

figure 5.

General Chemical Constituents

Analytical results of field blanks for water

years 1995–96 for general chemical constituents are

listed in table 17. Any concentration that was greater

than twice the laboratory reporting limit is shown

in a shaded cell. Silica and, to some extent, chloride

indicate some systematic contamination. The silica

contamination can for the most part be explained

as the result of the use of contaminated blank water.

Independent analyses of the lots of blank water

used at French, East, and State Line sites showed

silica concentrations of 0.11 mg/L. Analyses of

the lots of blank water suspected of being used at

Gore and Dotsero showed a silica concentration of

0.30 mg/L (lot numbers were not recorded for these

Table 16. Summary of differences between post-processing split-replicate samples for nutrients and organic carbon

[Lowest rounding unit is equal to magnitude of the lowest significant figure]

Constituent Percent of samples

with no difference

Percent of samples

within plus or minus 1

lowest rounding unit

Percent of samples

within plus or minus 2

lowest rounding unit

Ammonia 100 100 100

Dissolved ammonia plus organic 100 100 100

Total ammonia plus organic 62 88 88

Nitrite 100 100 100

Nitrite plus nitrate 38 62 75

Dissolved organic carbon 43 72 86

Dissolved phosphorus 50 75 100

Total phosphorus 25 62 75

Orthophosphate 88 100 100
32 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

samples). Interpretation of the silica data collected

at network sites should not be affected by the silica

blank results because the contamination was introduced by the blank water.

The systematic chloride contamination source

might be due to incomplete flushing of the dilute

hydrochloric acid cleaning solution from the conesplitter outlet ports. Except for the one high

value at the State Line site, the contamination is

on the order of a few tenths of a milligram per liter

(table 17). Chloride concentrations for the environmental samples within the study unit range from 0.1 to

240 mg/L (U.S. Geological Survey, 1996, 1997). The

interpretation of the environmental data for sites with

low chloride concentrations, collected during the

period of contamination, will need to be qualified.

For future processing, the cone-splitter ports were

fully disassembled for rinsing, and further chloride

contamination has not been observed. All of

the other constituents appear to have little or no

contamination.

Nutrients and Organic Carbon

Analytical results of field blanks for water

years 1995–96 for nutrients, dissolved organic carbon,

and suspended organic carbon are listed in table 18.

Constituents listed in table 18 show little or

no contamination. Any concentration that was

greater than twice the laboratory reporting limit

is shown in a shaded cell. Results of the dissolved

organic carbon blanks show concentrations in the

0.1 to 0.3 mg/L range. The South Platte NAWQA

study unit also had dissolved organic carbon

blanks with similar detections (Robert Kimbrough and

Dennis Smits, U.S. Geological Survey, oral commun.,

1997). Increasing the amount of blank water used to

leach the suspended organic filter prior to processing

GUNNISON

TUNNEL

GUNNISON NEAR

GRAND JUNCTION

STATE LINE

EAST

DOTSERO

GORE

FRENCH

DRY

BAKER

DATE

SAMPLING SITES

1994 1995 1996

O N D J FMA M A J FMA MJJ ASO S N D J J

Figure 5. Distribution of collection of field blanks, 1995–96.
QUALITY-CONTROL SAMPLING PROGRAM 33

Table 17. Field blanks for general chemical constituents[Shaded cells represent concentrations greater than twice the laboratory reporting limit; mg/L, milligrams per liter; μg/L, micrograms per liter; <, concentration less than 

Site Date Calcium (mg/L) Magnesium (mg/L) Sodium (mg/L) Potassium (mg/L) Sulfate (mg/L) Chloride (mg/L) Fluoride (mg/L) Silica (mg/L) Iron (μg/L) 

State Line 042396 0.03 <0.01 <0.2 <0.1 <0.1 3.9 <0.1 0.09 <3 Dotsero 032096 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 0.33 <3 Gunnison near Grand Junction 121295 <0.02 <0.01 <0.2 <0.1 <0.1 0.3 <0.1 <0.01 <3 Gunnison Tunnel 121394 <0.02 <0.01 <0.2 0.2 <0.1 <0.1 <0.1 <0.01 <3 Gunnison Tunnel 062995 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 <0.01 <3 Gunnison Tunnel 082395 <0.02 <0.01 <0.2 <0.1 <0.1 0.3 <0.1 0.01 <3 East 082396 0.03 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 0.15 <3 Gore 102495 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 0.38 <3 French 052296 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 0.09 <3 Dry 011696 0.06 0.02 0.2 0.1 0.3 0.8 <0.1 0.01 <3 Baker 081895 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 <0.01 5 Baker 022796 <0.02 <0.01 <0.2 <0.1 <0.1 <0.1 <0.1 0.22 <3 Number of samples with concentrations

greater than twice the lab reporting limit

1000 14061 

Table 18. Field blanks for nutrients and organic carbon

[Shaded cells represent concentrations greater than twice the laboratory reporting limit; mg/L, milligrams per liter; <, concentration less than the laboratory reporting limi

Site Date Ammonia (mg/L)

Ammonia

plus

organic

(mg/L)

Total

ammonia

plus

organic

(mg/L)

Nitrite

(mg/L)

Nitrite

plus

nitrate

(mg/L)

Dissolved

organic

carbon

(mg/L)

Suspended

Organic

Carbon

(mg/L)

Phosphorus

(mg/L)

p

State Line 042396 <0.02 <0.2 <0.2 <0.01 <0.05 -- -- <0.01 Dotsero 032096 <0.02 <0.2 <0.2 <0.01 <0.05 0.2 0.1 <0.01 Gunnison near Grand Junction 121295 <0.02 <0.2 <0.2 <0.01 <0.05 0.3 0.1 <0.01 Gunnison Tunnel 121394 <0.02 <0.2 <0.2 <0.01 <0.05 0.2 0.1 <0.01 Gunnison Tunnel 062995 <0.02 <0.2 <0.2 <0.01 <0.05 0.1 0.1 0.01 Gunnison Tunnel 082395 <0.02 <0.2 <0.2 <0.01 <0.05 0.1 -- <0.01 East 082396 <0.02 <0.2 <0.2 <0.01 <0.05 -- -- 0.01 Gore 102495 <0.02 <0.2 <0.2 <0.01 <0.05 0.1 0.1 <0.01 French 052296 0.02 <0.2 <0.2 <0.01 <0.05 0.1 <0.1 <0.01 Dry 011696 <0.02 <0.2 <0.2 <0.01 <0.05 0.2 0.1 <0.01 Baker 081895 <0.02 <0.2 <0.2 <0.01 <0.05 0.2 0.1 <0.01 Baker 022796 <0.02 <0.2 <0.2 <0.01 <0.05 0.3 0.1 <0.01 Number of samples with concentrations

greater than twice the lab reporting limit

0 0 0 00 2 0 0 
34 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality

Assessment Study Unit, Water Years 1995–96

the sample may reduce the concentrations measured in

these blanks. Future processing methods will include a

100 ml (milliliter) blank-water rinse.

CONCLUSIONS

Quality-control samples provide part of the

information needed to estimate the bias and variability

that result from sample collection, processing, and

analysis. This report discusses the quality-control

samples of surface water collected during water

years 1995–96 in the UCOL study unit. Initial design

of the quality-control plan incorporated the expected

and measured constituent concentrations, streamflow

conditions, and land use to distribute samples within

the network. Results of the analysis of pre-processing

split-replicate, concurrent-replicate, sequentialreplicate, and post-processing split-replicate qualitycontrol samples indicate that variability resulting

from sample collection, processing, handling, shipping, and analysis generally is low and will have no

practical effect on environmental data interpretation.

No large systematic increase in variability resulting

from sample collection or processing is evident in

the results of the analysis. Analysis of field-blank

samples indicated that, with the exception of chloride

and silica, no systematic contamination of samples is

apparent. Interpretation of the chloride environmental

data will need to be qualified by reference to the

chloride blank contamination. The silica contamination was the result of silica in the blank water and

will not affect interpretation of environmental data.

Data analysis presented in this report has

resulted in the following procedural changes for

sampling within the UCOL surface-water network:

(1) Fully disassemble the fittings and tubing of the

outlet ports of the decaport sample splitter during field

cleaning and rinsing; (2) implement recording and

tracking of lot numbers and certificate of analyses for

water used as blank water; (3) leach dissolved organic

carbon filters with at least 100 ml of organic blank

water prior to processing the sample (smaller volumes

were previously used); (4) process additional field

blanks and replicates for trace-element constituents

(few samples available to date); and (5) test the efficiency of the field cleaning protocol by processing

blanks after field-cleaning equipment rather than using

laboratory-cleaned equipment. These changes were

implemented in water year 1997.

REFERENCES CITED

Apodaca, L.E., Driver, N.E., Stephens, V.C., and Spahr,

N.E., 1996, Environmental setting and implications

on water quality, Upper Colorado River Basin,

Colorado and Utah: U.S. Geological Survey

Water-Resources Investigations Report 95–4263,

33 p.

Driver, N.E., 1994, National Water-Quality Assessment Program-Upper Colorado River Basin:

U.S. Geological Survey Open-File Report 94–102,

2 p.

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990,

Implementation plan for the National Water-Quality

Assessment Program: U.S. Geological Survey OpenFile Report 90–174, 10 p.

Spahr, N.E., Driver, N.E., and Stephens,V.C., 1996,

The Upper Colorado River National WaterQuality Assessment Program surface-watermonitoring network: U.S. Geological Survey Fact

Sheet FS–191–96, 4 p.

U.S. Geological Survey, 1996, Water resources data,

Colorado, water year 1995—v. 2, Colorado

River Basin: U.S. Geological Survey Water-Data

Report CO–95–2, 471 p.

———1997, Water resources data, Colorado, water